There are numerous methods to produce an optical device including an optical die, such as a vertical-cavity surface-emitting laser (VCSEL). But in all cases they require four connections: the optical, the electrical, the thermal and the mechanical. Different applications require different approaches on how to balance these four connections.
When an optical device is produced, an optical die is mounted on and connected to a carrier. The mounting of an optical die to a carrier and coupling of light to optical fibres are both time consuming steps requiring micromechanical piece parts. Consequently, these steps are high cost steps in the production of an optical device.
FIG. 1 illustrates an optical device comprising a transparent glass carrier 101 with a metalized pattern 102 for electrical connection and pads for epi down attachment of an optical die 103. The light 104 passes through the glass substrate 101. The position of the optical die 103 with respect to the metal pattern of the carrier is determined by self-alignment. For example, surface tension in liquid phase solder joints 105 could be used.
FIG. 2 illustrates an optical assembly comprising of an optical die 103 attached to a silicon carrier 106 with a groove 107 for fibre alignment. At the end of the groove there is a metalized mirror 108 reflecting the light 90 degrees (45 deg mirror) from/to optical die 103 to fibre end face 109.
One way to address the cost problem is to apply wafer scale methods to produce an optical device. Using a wafer scale method, a number of integrated circuits can be attached at the same time on a common slice of wafer. Once the fabrication process is complete, the wafer is divided into the individual devices.
However, each optical device needs to be tested prior to shipping. From a cost perspective, it is beneficial if the optical devices can be tested at the wafer scale stage (ie: before the wafer is divided into individual devices).